The present application relates to the field of radiation imaging systems. It finds particular application to correcting projection data generated from a computed tomography (CT) examination of an object and/or for computing CT values of an object or sub-objects thereof from the projection data.
Computed tomography (CT) systems and other radiation imaging modalities, are useful to provide information, or images, of interior aspects of an object under examination. Generally, the object is exposed to radiation comprising photons (e.g., x-rays, gamma rays, etc.), and an image(s) is formed based upon the radiation absorbed and/or attenuated by interior aspects of the object, or an amount of radiation photons that is able to pass through the object. Generally, highly dense aspects of the object absorb and/or attenuate more radiation than less dense aspects, and thus an aspect having a higher density, such as a bone or metal, for example, may be apparent when surrounded by less dense aspects, such as muscle or clothing.
CT systems may be configured as single energy radiation imaging systems or multi-energy (e.g., dual-energy) radiation imaging systems. Although commonly referred to as a single energy radiation system, single energy radiation imaging systems are typically configured to use a single spectrum of radiation photon energy to generate (e.g., reconstruct) an image(s) of an object. Respective voxels of a three-dimensional image produced by a single energy radiation imaging system represent a CT value which is based upon the density of the object represented by the voxel. Multi-energy radiation imaging systems are configured to use multiple, distinct radiation photon energy spectra to generate an image(s) of an object. Respective voxels of a three-dimensional image produced by a multi-energy radiation imaging system may represent a CT value, which is based upon the density of the object represented by the voxel, and/or a z-effective value, which is based upon the atomic composition of the object. To capture data from multiple, distinct energy spectra, the multi-energy radiation imaging system may be configured to emit multiple, distinct energy spectra or the detector array may be configured to filter the impinging radiation photons (e.g., emitted across a single energy spectrum) based upon energy (e.g., dividing an emitted energy spectrum into a plurality of smaller energy spectra).
During generation (e.g., reconstruction) of images produced by single energy radiation imaging systems and/or multi-energy radiation imaging systems, image artifacts may be introduced due to, among other things, inherent phenomena that occur due to the interaction of radiation and objects. For example, radiation interacting with two objects of a same density and atomic composition may scatter differently based upon the shape of respective objects, objects surrounding each object, etc. As another example, objects having a higher density and/or atomic number may reflect or absorb a disproportionate amount of radiation in a low range(s) of the emitted radiation spectrum or spectra. This later phenomenon is sometimes referred to as beam hardening.
Image artifacts may cause an object to appear to have a different density and/or atomic composition than its true density and/or atomic composition. Such differences may result in false positives and/or false negatives during an inspection of the image by personnel and/or by object detection software configured to identify objects of interest (e.g., threat objects, malignant growths, etc.), for example.